A thermal imager typically works like a thermometer with a sensor array: it measures how much each pixel heats up and turns that into a picture. But this method has a limit — the device's own noise obscures faint heat.
A conventional thermal camera is like a thermometer that slowly heats up and cools down. It shows where heat is well, but it can't keep up with fast motion. The new sensor works differently: it counts individual quanta of heat, like a droplet counter during rain.